3 ms·

Most deep-space probes use storable hypergolics (hydrazines + nitrogen tetroxide). Some of the crazy parts of this book actually came true! (I don't intuitivel

Most deep-space probes use storable hypergolics (hydrazines + nitrogen tetroxide). Some of the crazy parts of this book actually came true! (I don't intuitively understand how the JWST has $10 billion precision optics and hypercorrosive oxidizers right next to each other, and nothing bad happens. Engineering baffles me).

colechristensen 4y ago
The propellant tanks don’t leak, the combustion products aren’t corrosive. Designing spacecraft is like “does this material ever outgas anything which might affect other parts? I guess we can’t use it” much less leaky propellant tanks.
- robocat 4y ago
  > the combustion products aren’t corrosive Nitpick: if the chemical combustion is perfectly efficient, there are no corrosive byproducts or remainder.
  - bernulli 4y ago
    Nitnitpick: and we know it isn’t and the corrosive propellants will contaminate surfaces: https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf
DylanSp 4y ago
Not just deep-space probes; Dragon, Orion, and I think Starliner all use hypergols. Plenty of satellites do as well, though I think there's a trend towards using various sorts of electric propulsion. Really, the big misprediction of the book (looking at chapter 13, "What Happens Next") is that it doesn't consider missiles (and some upper/deep-space stages) moving to solid propellant; but it's a book about liquid propellants, so I'm not too surprised.
bernulli 4y ago
Absolutely! I’m sure they analyzed for that, but backflow to the opposite direction of the nozzle is quite unintuitive but normal in rarefied flow, with propellant deposition next to the nozzle possible and documented [1]. Just because you point it away from the sensitive stuff does not mean it won’t get there and leave nasty traces. [1] https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf

colechristensen 4y ago

The propellant tanks don’t leak, the combustion products aren’t corrosive. Designing spacecraft is like “does this material ever outgas anything which might affect other parts? I guess we can’t use it” much less leaky propellant tanks.

robocat 4y ago
> the combustion products aren’t corrosive Nitpick: if the chemical combustion is perfectly efficient, there are no corrosive byproducts or remainder.
- bernulli 4y ago
  Nitnitpick: and we know it isn’t and the corrosive propellants will contaminate surfaces: https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf

DylanSp 4y ago

Not just deep-space probes; Dragon, Orion, and I think Starliner all use hypergols. Plenty of satellites do as well, though I think there's a trend towards using various sorts of electric propulsion. Really, the big misprediction of the book (looking at chapter 13, "What Happens Next") is that it doesn't consider missiles (and some upper/deep-space stages) moving to solid propellant; but it's a book about liquid propellants, so I'm not too surprised.

bernulli 4y ago

Absolutely! I’m sure they analyzed for that, but backflow to the opposite direction of the nozzle is quite unintuitive but normal in rarefied flow, with propellant deposition next to the nozzle possible and documented [1]. Just because you point it away from the sensitive stuff does not mean it won’t get there and leave nasty traces. [1] https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/a588174.pdf